DESCRIPTION (copied from Applicant Abstract): The cell biology of eukaryotic cells is dominated by compartmentation of the cell into different organelles and regions. The fatty acids that compose the hydrophobic core of each membrane are predicted to affect cell function and the biology of the whole organism through their influence on the fluidity of the membrane and the overall shape of the glycerolipid molecules of which they are part. Despite our appreciation of these physical principles, little is known in animals about the mechanisms through which fatty acids affect life processes. We have cloned the extended family of fatty acid desaturase genes in Caenorhabditis elegans and characterized the enzymes that they encode. We have also isolated mutants defective in at least five desaturation steps and begun the characterization of striking phenotypes that are observed in them. We are now poised to take full advantage of the classical, molecular, and reverse genetic approaches available in C. elegans to test new hypotheses about specific mechanisms through which the shape and physical properties of fatty acid molecules impact the cell biology and physiology of animals. Three hypotheses will be examined: (1) That a deficit of polyunsaturated acids limits the production of non-bilayer lipids required for synaptic vesicle formation. This proposition is supported by preliminary behavioral and pharmacological studies. Ultrastructural examination tests of genetic interaction with known neurotransmission mutations will test the hypothesis further. (2) That a lethal defect in cell fusion during embryogenesis is caused by greatly reduced membrane fluidity. Biochemical complementation of this defect has been achieved. The isolation of multiple mutants and suppressors, together with studies on the effect of temperature on this phenotype will provide data that can be correlated to measurements of membrane fluidity. (3) That decreased membrane unsaturation compromises growth and viability at low temperatures while providing a modest increase in thermotolerance. Evaluating the possible role of desaturases will include estimates of desaturase expression at different temperatures. Quantitative measures of low-temperature performance and thermotolerance of the range of desaturase mutants will be correlated with fatty acid composition and measurements of membrane fluidity.